1. Field of the Invention
The present invention relates generally to hand tools. More specifically, the present invention relates to a device for locating ferromagnetic objects.
2. Description of the Prior Art
It is often necessary to locate structural support members that are hidden behind a wall, ceiling, or floor covering material. These support members include wall studs, floor joists, beams, roof rafters, and strapping. The support members may be wood, as are commonly used in residential construction, or metal, as are commonly used in commercial construction.
Wall or ceiling coverings are secured to structural support members using ferromagnetic fasteners such as screws or nails that are driven through the covering and into the supporting members underneath. For example, drywall sheets are secured with fasteners to framing members as part of a wall or ceiling. These fasteners are concealed with wall compound to finish the surface, thereby concealing the location of the underlying support members.
It is also often necessary to find ferromagnetic fasteners in stand-alone pieces of wood or other non-magnetic substances. For example, prior to using a planer, saw, or other machine on a loose piece of (used) wood, it is desirable to locate ferromagnetic fasteners in the wood to prevent metallic fasteners from causing damage to the machine.
A ferromagnetic material is a material having magnetic properties similar to those of iron. Simply put, one can make a magnet out of a ferromagnetic material. Ferromagnetic materials include iron, nickel, cobalt, and alnico (an aluminum-nickel-cobalt alloy).
During construction, the locations of structural supports are known to the installer in order to properly secure the covering with fasteners. The fasteners are then concealed during the finishing process. It is often necessary to know the location of structural members in order to perform repair work or to securely hang heavy items. One can discover the location of structural members by locating the member itself, or by locating the fasteners attached to structural members.
Locating devices or “stud finders” have been used to locate the presence of structural members within walls and ceilings. Active electronic devices and passive magnetic devices are types of devices used to find structural members in building construction. Active electronic devices use waves that permeate a wall, ceiling, or floor covering. By detecting a change in density when the user moves it from a low density section of wall (no support structure) to a higher density area (possible support structure), these electronic devices indicate the location of a structural member. For active electronic devices to function properly, however, the user must calibrate the device on an area of the wall that does not have support structures (e.g., studs). In other words, the user must calibrate the device over a low density area of the wall.
Passive magnetic devices are relatively accurate since they depend on the fact that most coverings are secured in place by means of metal fasteners that are driven into support members through a wall, floor, or ceiling covering. Since the location of these fasteners is the same as the location of the support structures, magnetic stud finders are used to reveal their location. For example, one device has a housing with pivot bosses to pivotably support a magnet assembly in a location where it can be influenced by the nearby presence of magnetic metals such as steel nails. When the device is out of the magnetic influence of a steel nail, the magnet assembly is rotated to a random angle that remains substantially constant while the user moves the stud finder. When the user moves the stud finder into close proximity to a steel nail, the magnet assembly rotates about the pivot boss until its longitudinal axis points towards the steel nail. The location of the steel nail is verified by moving the stud finder past the steel nail and noting that the magnet assembly rotates to maintain its axis to point towards the steel nail.